For the general public, the question of whether genes contribute to a person’s intelligence is a matter of controversy. Among intelligence researchers, there is no doubt that variation in intelligence is partly attributable to genes. In fact, the purpose of the very first twin study, done back in 1924, was to study the contribution of genes to intelligence.

Today, researchers can predict how similar the IQ scores of people will be based on how similar their genes are. Such work has confirmed what twin studies have long shown: In adulthood, the majority of variation in intelligence is caused by genes. We now know about many genes that can be used to predict intelligence. Geneticists can determine which version of these genes someone has and, based on how many IQ-enhancing and IQ-deflating gene variants there are, assign a “polygenic score” (a score based on the effect of many genes) that correlates at about 0.3 with IQ scores, which is moderate by conventional standards.

If ancient DNA is sufficiently well preserved, we can make similar comparisons between people who are alive today and people who lived thousands of years ago. This would be an interesting way to judge the extent to which the history of human progress may be the history of the biological evolution of intelligence. Of course, in some sense, everyone knows the two are related. Humans have evolved to be more intelligent than chimps; we have great civilizations and chimps do not. However, many people think that important genetic changes to humans stopped around 100,000 years ago, or that evolution is so slow that even if it has not stopped, the difference between now and then is negligible.

In fact, standard equations from population genetics suggest that evolution can have significant effects in five or ten generations. Sophisticated analysis can determine the relative ages of different genetic clusters in the modern human genome, and such studies have shown that ever since the Neolithic Revolution of approximately 10,000 years ago, the human genome has been changing 100 times faster than what normally occurred during evolution. It was only after the Neolithic Revolution that important traits such as lactose tolerance and the white skin of Europeans appeared. It is therefore reasonable to suggest that our genetic potential for intelligence may have changed recently, too.

This was the focus of a recent paper by Dr. Michael Woodley and his colleagues. First, they tested the DNA of 99 ancient Eurasians who lived between 2540 B.C. and 809 A.D. to determine their “polygenic scores” for intelligence, based on three sets of genes known to predict intelligence. They then compared these scores to a sample of contemporary Europeans. For all three sets of genes, modern genomes had a higher polygenic score. The ratio of IQ-enhancing gene variants to IQ-depressing gene variants was higher in contemporary European genomes than in ancient ones. This strongly suggests that modern Europeans have higher genotypic intelligence. Dr. Woodley’s team found a positive correlation between the age of an ancient genome and its polygenic score, which suggests that genotypic IQ increased somewhat linearly over time.

Why would Europeans have evolved to be smarter than they were 2,000 years ago? At the group level, populations of smarter people may have been more likely to make technological innovations which helped them outfight and outbreed other groups. At the individual level, we know today that IQ is an excellent predictor of job performance as well as scientific innovation, so there is reason to think it might have been true then, too.

More productive people are often wealthier, and if intelligence led to wealth in the past as it does today, it probably led to longer lives and larger families. The work of economist Gregory Clark demonstrates that this was the case for much of English history. During the centuries preceding the Industrial Revolution, differential survival and fertility rates led to poor people being bred out of the population and replaced by the sons and daughters of the wealthy. Prof. Clark argues that this eugenic process partly explains why the Industrial Revolution took place in the West rather than somewhere else.